The present invention relates to a turbine plant and, more particularly, to a reheat steam turbine plant having a turbine bypass system which enables an improving of the operational characteristics of the turbine plant. In, for example, Japanese Patent Laid Open Application No. 26765/1984, a reheat steam turbine power plant is proposed including a turbine bypass system wherein an entire quantity of the steam, generated by the superheat of the boiler, is passed through a reheater of the boiler during a turbine bypass operation. The steam flows at a higher rate than the necessary flow rate for the reheater to be cooled so that a capacity of the turbine bypass system must be greater than otherwise required. However, it is uneconomical and ineffective to provide a large capacity for the turbine bypass system, since problems occur such as, for example, the passing of an unnecessarily large quantity of low temperature steam causes a delay in the temperature rise of the reheating steam when the power plant is started.
In, for example, "Modern Power Systems", July /Aug. 1983, a two stage reheat steam turbine power plant is proposed having a bypass system wherein the whole quantity or volume of steam generated by the superheater of the boiler, when passing through a first reheater and a second reheater, flows at a higher flow rate than the necessary flow rate for the reheaters to be cooled. Consequently, a disadvantage of this proposal resides in the fact that the capacity of the turbine bypass system must be larger than required. Thus, this proposed construction is also uneconomical and ineffective since it is necessary to provide a large capacity for the turbine bypass system. Additionally, in this proposed power plant, the temperature of the reheating steam cannot be quickly increased, so that a low temperature reheat steam is produced causing a delay in the start-up time of the power plant.
In, for example, Japanese Utility Model Laid Open Application No. 12604/1983, a two stage reheat steam turbine power plant is also proposed having a turbine bypass system, wherein the whole quantity of steam generated in the superheater flows into the reheaters through turbine bypass pipes, with the quantity of the reheat steam passed through the reheaters being increased by adding desuperheater water into the turbine bypass line for desuperheating the steam passing through the turbine bypass line. That is, the feed water to be added is turned into steam by a heat exchange with the high temperature steam passing through the turbine bypass pipes. During a start up operation of this proposes steam power plant, it is assumed that the quantity of steam generated in the superheater is 180 kg/sec, with the quantity of reheat steam passing through the first reheater reaching 200 kg/sec by adding the desuperheater water in the high pressure turbine bypass pipe, and the quantity of reheat steam passing through the second reheater reaches 220 kg/sec by adding the desuperheater water in the medium pressure turbine bypass pipe. By virtue of this arrangement, it takes more than forty minutes prior to the admission of steam into the steam turbine from the boiler ignition. Additionally, in Japanese Utility Model Laid Open Application No. 12604/1983, a further two stage reheat steam turbine power plant is proposed which includes a turbine bypass system, wherein both inlets of the first and second reheaters and outlets of the first and second reheaters are connected to each other by pipes. A disadvantage of this proposed construction resides in the fact that, in the operation of the turbine bypass system, it is difficult to control a valve located in a pipe line connecting an inlet and outlet of the first and second reheater without causing a temperature differential and pressure of the first and second cold reheating steam, and of the first and second hot reheating steam.
In Japanese Patent Publication No. 26765/1984, a turbine is proposed which includes a dump line connected from a cold reheat pipe to a condenser. However, the dump line is installed for maintaining a vacuum inside a high pressure turbine while the power plant is in an auxiliary operation, with the purpose of maintaining the vacuum inside the pressure turbine being to prevent the turbine blades from overheating which would be caused by a rotating of the turbine blades in air. While the dump line is a branch pipe of the cold reheat pipe, which is connected at an upstream side above a check valve attached on a cold reheat pipe, it is still not possible to reduce the capacity of the turbine bypass system by this proposed construction.
The aim underlying the present invention essentially resides in providing a steam turbine plant with a bypass system, wherein an arrangement is provided for enabling a control of the reheat steam through the reheater at an adequate range during operation of the turbine bypass system of the reheat steam turbine plant.
In accordance with advantageous features of the present invention, the heating of the reheat steam during the operation of the turbine bypass system is accelerated in order to reduce the starting time of the reheat steam turbine plant.
It is also possible in accordance with the present invention to accelerate the cooling of the reheat steam during the operation of the turbine bypass system in order to prevent an overheating of the reheat steam turbine.
In accordance with the present invention, a reheat steam turbine power plant is provided which includes a boiler having a superheater and a reheater therein, a turbine bypass system and means for regulating or controlling at least one of a steam flow rate or steam pressure, with the regulating or control means being adapted to control the steam flowing into the reheater at a suitable steam condition while the turbine bypass system is operating.
By virtue of the features of the present invention, it is possible to reduce the capacity of the turbine bypass system such that such capacity is less than the whole quantity of steam generated in the superheater, and to shorten the starting time of the reheat steam turbine power plant.